MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
16-6
Freescale Semiconductor
16.3.2.1.1
Finding Reset Configuration Half Word
The BAM searches the internal flash memory for a valid reset configuration halfword (RCHW). A valid
RCHW is a 16-bit value that contains a fixed 8-bit boot identifier and some configuration bits (see
Section 4.4.3.5.1, “Reset Configuration Half Word Definition
”). The RCHW is expected to be the first
halfword in one of the low address space flash blocks as shown in
.
BOOT_BLOCK_ADDRESS is the first address from
, where the BAM program finds a valid
RCHW.
If the BAM program does find a valid RCHW, the watchdog is enabled with the RCHW[WTE] bit, the
BAM program fetches the reset vector from the address of the BOOT_BLOCK_A 0x4, and
branches to the reset boot vector. A user application should have a valid instruction at the reset boot vector
address.
Figure 16-4. Reset Boot Vector
The watchdog timeout is set to 2.5
2
17
system clock periods if the watchdog is enabled.
16.3.2.2
External Boot Modes Flow.
The external boot mode is used to boot a user application from an external asynchronous memory that is
connected to the MCU external bus; it is controlled by CS0.
16.3.2.2.1
External Boot MMU Configuration
As shown in
, the BAM program sets up the two MMU regions differently than in internal flash
boot mode. The internal flash logical address space is mapped to the physical addresses of the EBI.
Table 16-4. Low Address Space (LAS)
Block Memory Addresses
Block
Address
0
0x0000_0000
1
0x0000_4000
2
0x0001_0000
3
0x0001_C000
4
0x0002_0000
5
0x0003_0000
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
A16
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
BOOT_BLOCK_A 0x0000_0004
Summary of Contents for MPC5553
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